Washington (CNN) - Officials at the Internal Revenue Service knew in June 2011 that their agents were targeting conservative groups for additional scrutiny on tax documents, an inspector general report to be released this week is expected to say, according to a congressional source familiar with the inquiry.

Further, an early timeline of events compiled by the inspector general and obtained by CNN indicates the agency's practice of singling out conservative groups began as early as March 2010, and in July of that year, unidentified managers within the agency "requested its specialists to be on the lookout for tea party applications." In August, specialists were warned to be on the lookout for "various local organizations in the tea party movement" applying for tax-exempt status. The specific criteria would change several times over the next two years, according to a portion of the report.FULL POST